Starting and overload control for split-phase electric motor



lap

March 19, 1957 SPLIT-PHASE ELECTRIC MOTOR Filed July 15. 1953 I H. F. CLARK STARTING AND OVERLOAD CONTROL FOR 268 BlME-TAL 58 BIMETAL BIMETAL IN VEN TOR.

hbrrEGadr His Armme United States Patent STARTING AND OVERLOAD CONTROL FOR SPLIT-PHASE ELECTRIC MOTOR Harry F. Clark, Dayton, Ohio, assiguor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application July 15, 1953, Serial No. 368,143

Claims. (Cl. 318221) This invention relates to electrical apparatus and more particularly to a control which may be used for controlling the starting of an electric motor and for overload protection.

It is an object of my invention to provide a simple compact control having few parts which is capable of performing both as a starting control and as an overload control for a split-phase electric motor.

It is another object of my invention to provide an ar- :rangement for both starting and overload controls in which a single toggle snap-acting means is arranged to provide snap-action operation of both the starting control and the overload control.

It is an object of my invention to provide an electrothermal starting and overload control in which the resetting of the overload control resets the starting control.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred form of the invention is clearly shown.

In the drawings:

Figure 1 is a view partly diagrammatic of a control embodying one form of my invention connected to a split phase motor with the control shown in the overload condition; and

Figure 2 is a view similar to Figure 1 with the control shown in the starting position.

Referring now to the drawings there is shown a thin rectangular base 20 of some suitable electrical insulating material. This base 20 is also provided with an L-shaped crib 22 also of electrical insulating material. Mounted on this base 20 is a first contact 24 adapted to be connected by the conductor 26 to the phase winding 28 of :an electric motor 30. The main junction of the main winding 32 and the phase winding 28 is connected to a :control switch 34 which in turn is connected to one side .36 of a single phase alternating current power supply. The other terminal of the main winding 32 is connected by a conductor 38 to an L-shaped terminal 40. This terminal 40 together with the base'portion of the overload bimetal strip 42 are riveted by the rivet 44 to the rib 22 as shown.

The other supply conductor 46 is connected to the terminal 48. From the terminal 48 there extends a ribbon heater 50 toward the rib 22. The heater 50 has its end portion beneath the cantilever bimetal strip 52 having its base portion riveted to the rib 22 by the rivet 54. The bimetal strip 52 and the heater 50 are insulated from the overload bimetal strip 42 by being spaced from each other on the insulating rib 22. The bimetal strip 52 carries the oppositely facing contacts 56, one side of which is adapted to engage the contact 24 in the starting position as shown in Figure 2. In the starting position, the contact 58 provided on the free upper end of the overload bimetal 42 is in engagement with the contact 56 on the opposite side. The contacts 56 and 58 are sufiiciently thick to make this possible even though the 2 stop 66 is located between the adjacent ends of the bimetals 52 and 42.

Connected to the free end of the overload bimetal strip 42 is a C-shaped toggle spring 60 having a low rate and suflicient spring force to hold all of the contacts in engagement as shown in Figure 2. It also has sufiicient range of expansion with only a small reduction in spring force to act on the bimetal strip 42 in the position shown in Figure 2 and because of its low rate will provide snapaction movement throughout its range. The upper end of the O-shaped toggle spring 60 is pivotally connected to a hook-shaped compensating bimetal 62 having its lower end riveted by the rivets 64 to the vertical portion of the rib 22. The bimetals 62 and 42 both tend to bow to the right when heated as does the bimetal strip 52. The base 20 is provided with a first stop 66 for limiting the movement of the strip 52 away from the contact 24. This permits the separation of the contacts 24 and 56 but permits the continued-engagement of the contacts 56 and 58. The base 20 is also provided with a second stop 68 which limits the movement of the overload bimetal 42 away from the starting bimetal 56 and the contact 24.

When the bimetals 42 and 52 as well as the heater 50 are cold, the bimetals will assume the position shown in Figure 2 which will close the circuit to both the main and phase windings 32 and 28. The current flows from the conductor 46 through the terminal 48 and the heater 50 to the base of the starting bimetal 56 and thence up the starting bimetal 52 to the double contact 56. From the double contact 56 a part of the current flows through the contact 24 and the conductor 26 to the phase winding 28 while the remainder of the current flows through the contact 58, the bimetal strip 42, the terminal 40 and the conductor 38 to the adjacent terminal of the main Winding 32. During the starting of the motor, the bimetal 52 heats up through flow of current through it and it is further heated by radiant heat from the heater 50. When this has continued long enough for the motor 30 to reach the balancing speed the bimetal 52 will be hot enough to snap from the position shown in Figure 2 away from the.

contact 24 to the position shown in Figure 1 against the stop 66. During the remainder of the running period of the motor 30, the heater 50 supplies sufficient radiant heat to the bimetal 52 to hold it against the stop 66.

The contact 58 will remain in contact with the contact 56 as long as the current flow through the main winding 32 and its circuit is within satisfactory limits. If this current flow is excessive either while the bimetal 52 is in the position shown in Figure 2 or While it is in the position shown in Figure 1 it will heat and bend away to carry the contact 58 away from the contact 56 to open the main winding circuit as shown in Figure 1. This opening movement continues until the overload bimetal 42 rests against the stop 63. This will disconnect the main winding circuit. The disconnection of the main winding circuit will cause the bimetal 42 to cool and when it is cooled sufliciently it will snap back toward the contact 24 and carry with it the double contact 56 and the starting bimetal 52 to the position shown in Figure 2.

Changes in the temperature of the environment air will change the rate of heating of the bimetals 42 and 52 but this is compensated by the deflection of the hook shaped compensating bimetal 62 a suflicient amount to compensate for the effect of environment temperatures on the bimetals 42 and 52. The bimetal 62 accomplishes this by moving to the right upon heating so as to increase the augularity of the C-shaped toggle spring.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted as may come within the scope of the claims which follow.

What is claimed is as follows:

1. A starting control for an electric motor having main and phase windings including a first contact adapted to be connected to the phase winding, a movable double contact adapted to make contact with andto be separated from said first contact, thermal operating'means for moving said double contact away from said first contact upon heating, a second contact adapted to make contact with said double contact, means responsive to a motor current overload for moving said second contact away from said double contact, said second contact being adapted to be connected in series with the main winding, and means for heating said thermal operating means coincidentally to the energization of the phase winding.

2. A control including a first electrical contact, a first terminal connected to the first contact, a first bimetal strip means supported in position to make electrical contact with said contact when cool and to move away from said contact when heated. a second terminal connected to said first strip means, a second bimetal strip means supported in position to make electrical contact when cool with said first strip means and to move with and away when heated from said first strip means, a third terminal connected to said second strip means, and a stop means located in the path of movement of said first strip means sufiiciently near to its cool position for limiting its movement away from said first contact to a lesser amplitude of movement than the total amplitude of movement of said second strip means, said second strip means having a total amplitude of free movement sufiiciently greater than the maximum permitted amplitude of said first means by said stop means to move away from said first strip means after said first strip means has engaged said stop means.

3. A control including a first electrical contact, a first terminal connected to the first contact, a first bin-total strip means supported in position to make electrical contact with said contact when cool and to move away from said contact when heated, a second terminal connected to said first strip means, a second bimetal strip means supported in position to more electrical contact when cool with said first strip means and to move with and away when heated from said first strip means, a third terminal connected to said second strip means, and a stop means located in the path of movement of said first strip means sufiiciently near to its cool position for limiting its movement away from said first contact to a lesser amplitude of movement than the total amplitude of movement of said second strip means, a second stop means located in the path of movement of the second strip means sufiiciently far from its cool position to permit an amplitude of movement greater than the amplitude of movement permitted the first strip means by the first mentioned stop means.

4. A control including a first electrical contact, a first terminal connected to the first contact, a first bimetal strip means supported in position to make electrical contact with said contact when cool and to move away from said contact when heated, a second terminal connected to said first strip means, a second bimetal strip means supported in position to make electrical contact when cool with said first strip means and to move with and away when heated from said first strip means, a third terminal connected to said second strip means, a stop means located in the path of movement of said first strip means sufficicntly near-to its cool position for limiting its movement away from said first contact to a lesser amplitude of movement than the total amplitude of movement of said second strip means, a second stop means located in the path of movement of the second strip means sufficiently far from its cool position to permit an amplitude of movement greater than the amplitude of movement permitted the first strip means by the first mentioned stop means, a' toggle means operatively connected to said second strip means having such angularity and relationship to resiliently urge the secondstrip means toward the first strip means and said first contact and a compensating bimetal strip means operatively connected to said toggle means to change the angularity of said toggle means according to ambient temperature changes 5. A starting control for an electric motor having main and phase windings including a first contact adapted to be connected to the phase winding, a first bimetal means carrying a double contact having its high expanding faces on the side nearest the first contact and being located to carry the double contact into contact with the first contact when cool and away when heated, said first bimetal means being adapted to be connected to a snpply conductor, a second bimetal means carrying a contact having its high expanding face on the side nearest the first contact and being located to carry it into contact with said double contact when c001 and away when heated, said second bimetal means being adapted to be connected to said main winding, and a stop means located in the path of movement of said first bimetal means at a point sufiicient to limit its amplitude of movement to an amount less than the maximum amplitude of movement of said second bimetal means. 

